Re: [PATCH V4 0/2] mm: FAULT_AROUND_ORDER patchset performance data for powerpc

[Kirill A. Shutemov]

Andrew Morton wrote:
> On Mon, 19 May 2014 16:23:07 -0700 (PDT) Hugh Dickins <hu...@google.com> 
> wrote:
> 
> > Shouldn't FAULT_AROUND_ORDER and fault_around_order be changed to be
> > the order of the fault-around size in bytes, and fault_around_pages()
> > use 1UL << (fault_around_order - PAGE_SHIFT)
> 
> Yes.  And shame on me for missing it (this time!) at review.
> 
> There's still time to fix this.  Patches, please.

Here it is. Made at 3.30 AM, build tested only.

I'll sign it off tomorrow after testing.

diff --git a/mm/memory.c b/mm/memory.c
index 037b812a9531..9d6941c9a9e4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3402,62 +3402,62 @@ void do_set_pte(struct vm_area_struct *vma, unsigned 
long address,
        update_mmu_cache(vma, address, pte);
 }
 
-#define FAULT_AROUND_ORDER 4
+#define FAULT_AROUND_BYTES 65536
 
 #ifdef CONFIG_DEBUG_FS
-static unsigned int fault_around_order = FAULT_AROUND_ORDER;
+static unsigned int fault_around_bytes = FAULT_AROUND_BYTES;
 
-static int fault_around_order_get(void *data, u64 *val)
+static int fault_around_bytes_get(void *data, u64 *val)
 {
-       *val = fault_around_order;
+       *val = fault_around_bytes;
        return 0;
 }
 
-static int fault_around_order_set(void *data, u64 val)
+static int fault_around_bytes_set(void *data, u64 val)
 {
-       BUILD_BUG_ON((1UL << FAULT_AROUND_ORDER) > PTRS_PER_PTE);
-       if (1UL << val > PTRS_PER_PTE)
+       BUILD_BUG_ON(FAULT_AROUND_BYTES / PAGE_SIZE > PTRS_PER_PTE);
+       if (val / PAGE_SIZE > PTRS_PER_PTE)
                return -EINVAL;
-       fault_around_order = val;
+       fault_around_bytes = val;
        return 0;
 }
-DEFINE_SIMPLE_ATTRIBUTE(fault_around_order_fops,
-               fault_around_order_get, fault_around_order_set, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fault_around_bytes_fops,
+               fault_around_bytes_get, fault_around_bytes_set, "%llu\n");
 
 static int __init fault_around_debugfs(void)
 {
        void *ret;
 
-       ret = debugfs_create_file("fault_around_order", 0644, NULL, NULL,
-                       &fault_around_order_fops);
+       ret = debugfs_create_file("fault_around_bytes", 0644, NULL, NULL,
+                       &fault_around_bytes_fops);
        if (!ret)
-               pr_warn("Failed to create fault_around_order in debugfs");
+               pr_warn("Failed to create fault_around_bytes in debugfs");
        return 0;
 }
 late_initcall(fault_around_debugfs);
 
 static inline unsigned long fault_around_pages(void)
 {
-       return 1UL << fault_around_order;
+       return fault_around_bytes / PAGE_SIZE;
 }
 
 static inline unsigned long fault_around_mask(void)
 {
-       return ~((1UL << (PAGE_SHIFT + fault_around_order)) - 1);
+       return ~(round_down(fault_around_bytes, PAGE_SIZE) - 1);
 }
 #else
 static inline unsigned long fault_around_pages(void)
 {
        unsigned long nr_pages;
 
-       nr_pages = 1UL << FAULT_AROUND_ORDER;
+       nr_pages = FAULT_AROUND_BYTES / PAGE_SIZE;
        BUILD_BUG_ON(nr_pages > PTRS_PER_PTE);
        return nr_pages;
 }
 
 static inline unsigned long fault_around_mask(void)
 {
-       return ~((1UL << (PAGE_SHIFT + FAULT_AROUND_ORDER)) - 1);
+       return ~(round_down(FAULT_AROUND_BYTES, PAGE_SIZE) - 1);
 }
 #endif
 
@@ -3515,7 +3515,7 @@ static int do_read_fault(struct mm_struct *mm, struct 
vm_area_struct *vma,
         * if page by the offset is not ready to be mapped (cold cache or
         * something).
         */
-       if (vma->vm_ops->map_pages) {
+       if (vma->vm_ops->map_pages && fault_around_pages() > 1) {
                pte = pte_offset_map_lock(mm, pmd, address, &ptl);
                do_fault_around(vma, address, pte, pgoff, flags);
                if (!pte_same(*pte, orig_pte))
-- 
 Kirill A. Shutemov
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